The following question was posed to HaGaon HaRav Avigdor HaKohen Miller, zecher tzaddik l’vracha:
Is it better to daven a long Shemonah Esrei and to therefore miss kedusha?
The rav, zecher tzaddik l’vracha, responded:
Absolutely! But it depends however on what you’re thinking. If you’re thinking that I’m davening a long Shemonah Esrei in order to make a “hit” with those around me, then absolutely not. Some people do that, by the way. I see people doing that. But if you’re doing it because you want more time to think about what the words mean, then there’s no question that it’s a very good investment to daven with kavanah.